JP7456150B2 - brake control device - Google Patents

Description

The present disclosure relates to a brake control device.

Conventionally, there has been a technology called DAR (Drive Away Release) that releases the parking braking force in response to an acceleration operation to accelerate the vehicle when the vehicle is stopped due to the parking braking force generated by the electric parking brake. Are known. In such conventional technology, parking control is triggered when the driving force generated by the vehicle's drive source exceeds a predetermined threshold in response to an acceleration operation, assuming that all drive wheels of the vehicle are in contact with the ground. It is common to initiate power release.

Japanese Patent Application Publication No. 2015-536270

However, on a predetermined road surface such as an uphill road with many bumps, it is also assumed that the vehicle is stopped by the parking braking force with at least one wheel not in contact with the ground. If a floating wheel that is not in contact with the ground is the driving wheel, and the parking braking force is released using the general DAR as described above, the actual driving force that is sufficient to compensate for the decrease in parking braking force will not be transmitted to the road surface. , for example, there is a risk that unintended vehicle behavior may occur, such as sliding downhill on an uphill road.

Therefore, one of the problems of the present disclosure is to provide a brake control device that can suppress unintended vehicle behavior that may occur when the parking braking force is released in response to an acceleration operation.

A brake control device as an example of the present disclosure includes an acquisition unit that acquires the output of a sensor that detects information indicating the grounding state of the driving wheels of a vehicle, and an acquisition unit that acquires the output of a sensor that detects information indicating the ground contact state of the drive wheels of a vehicle, and a When an acceleration operation is performed to accelerate the vehicle, the ground contact state of the drive wheels is identified based on the output of the sensor acquired by the acquisition unit, and a control method that differs depending on the identified ground contact state is performed. and a control unit that controls the electric parking brake so as to release the parking braking force at the parking brake.

According to the brake control device described above, when releasing the parking braking force in response to an acceleration operation, the ground contact state of the driving wheels is taken into consideration. Therefore, it is possible to suppress unintended vehicle behavior that may occur when the parking braking force is released in response to an acceleration operation.

Furthermore, in the above-described brake control device, the control unit controls the parking braking force when the driving force generated by the drive source of the vehicle in response to the acceleration operation reaches a threshold value determined according to the ground contact state of the driving wheels. The electric parking brake is controlled to start releasing the parking brake. According to such a configuration, the timing to start releasing the parking braking force can be appropriately adjusted using the threshold value determined according to the ground contact state of the drive wheels so as to suppress unintended vehicle behavior. I can do it.

In addition, in the brake control device described above, the control unit adjusts the gradient of the release of the parking braking force according to the ground contact state of the drive wheels. With this configuration, for example, when at least one drive wheel is not on the ground, the parking braking force can be released more gradually than when all drive wheels are on the ground, and the parking braking force can be released with a gradient according to the ground contact state of the drive wheels so as to suppress unintended vehicle behavior.

Furthermore, in the brake control device described above, when the driving wheels include a floating wheel that is not in contact with the ground, the control section generates parking braking force on the driving wheels other than the floating wheel while continuously generating parking braking force on the floating wheel. The electric parking brake is controlled to release the parking braking force. According to such a configuration, for example, in a vehicle having an LSD (Limited Split Differential) function, driving force is prevented from being transmitted intensively only to the floating wheels, and is transmitted to the driving wheels that are on the ground. The driving force can be reliably transmitted.

In this case, the control unit controls the electric parking brake so that the floating wheel continues to generate a parking braking force until the floating wheel touches the ground, even when the vehicle starts moving. With this configuration, the driving force can be reliably transmitted to the driving wheels that are in contact with the ground, even when the vehicle starts moving.

Furthermore, in the brake control device described above, when an abnormality occurs in the sensor, the control section is configured to control the control section based on the output of the sensor acquired by the acquisition section at a past timing that satisfies the condition that the vehicle has not started up to the present. to determine the current ground contact status of the drive wheels. According to such a configuration, even if an abnormality occurs in the sensor, past data can be used to prevent unintended vehicle behavior that may occur when releasing the parking braking force in response to an acceleration operation. Can be suppressed.

FIG. 1 is an exemplary and schematic block diagram showing a schematic configuration of a vehicle according to an embodiment. FIG. 2 is an exemplary and schematic cross-sectional view showing the configuration of a brake device provided on a rear wheel of a vehicle according to an embodiment. FIG. 3 is an exemplary and schematic block diagram showing the functions of the brake control device according to the embodiment. FIG. 4 is an exemplary timing chart for explaining an example of releasing the parking braking force in response to an acceleration operation performed in the embodiment. FIG. 5 is an exemplary flowchart showing a series of processes that the brake control device according to the embodiment executes when releasing the parking braking force in response to an acceleration operation. FIG. 6 is an exemplary timing chart for explaining the release of parking braking force in response to an acceleration operation that may be performed in a modification of the embodiment.

Embodiments and modified examples of the present disclosure will be described below based on the drawings. The configurations of the embodiments and modified examples described below, as well as the effects and effects brought about by the configurations, are merely examples, and are not limited to the contents described below.

<Embodiment>
FIG. 1 is an exemplary and schematic block diagram showing a schematic configuration of a vehicle according to an embodiment. Below, as an example, an example in which the technology of the embodiment is applied to a four-wheeled vehicle having front wheels FL and FR and rear wheels RL and RR will be described. Furthermore, hereinafter, the front wheels FL and FR and the rear wheels RL and RR may be collectively referred to as wheels unless there is a need to distinguish them.

As shown in FIG. 1, the vehicle according to the embodiment includes a service brake 1 that generates braking force in response to a driver's depression of a brake pedal 3, and an EPB motor 10 that generates braking force separately from the service brake 1. It has two types of braking devices (braking force applying section): an electric parking brake 2 that generates the electric parking brake; The electric parking brake may also be referred to as EPB (Electric Parking Brake). Below, when it is necessary to distinguish between them, the braking force generated by the service brake 1 may be referred to as the service braking force, and the braking force generated by the electric parking brake 2 may be referred to as the parking braking force.

In the example shown in FIG. 1, the service brake 1 is configured to apply braking force to all of the front wheels FL and FR and the rear wheels RL and RR, and the electric parking brake 2 is configured to apply braking force to all the wheels, including the front wheels FL and FR and the rear wheels RL and RR. It is configured to apply braking force only to RR and RR. Although the details will be described later, both the service brake 1 and the electric parking brake 2 have a structure that applies braking force to the wheels by frictional force by pressing the brake pads 11 against the brake discs 12 that rotate together with the wheels. ing.

Although FIG. 1 shows, as an example, a configuration in which the electric parking brake 2 applies braking force only to the rear wheels RL and RR, the technology of the embodiment is such that the electric parking brake 2 applies braking force only to the front wheels FL and FR. It is also applicable to a configuration in which the braking force is applied to only one wheel, and it is also applicable to a configuration in which the electric parking brake 2 applies braking force to all wheels.

The service brake 1 includes a master cylinder 5 that generates pressure (hydraulic pressure) based on a brake operation such as depression of a brake pedal 3 by a driver, and a brake booster 4 that amplifies the force of the brake operation. . The service brake 1 transmits the hydraulic pressure in the master cylinder 5 corresponding to the depression force of the brake pedal 3 amplified by the brake booster 4 to the wheel cylinder 6 provided on each wheel, thereby applying hydraulic pressure control to the wheels. Give power.

Here, in the example shown in FIG. 1, a hydraulic pressure control circuit 7 is provided between the master cylinder 5 and the wheel cylinder 6. This hydraulic control circuit 7 includes a solenoid valve, a pump, etc., and is called ESC (Electronic Stability Control) for improving vehicle safety, such as adjusting the braking force of the service brake 1 according to the situation. Provided to realize control. The hydraulic control circuit 7 is driven under the control of an ESC-ECU (Electronic Control Unit) 8.

On the other hand, the electric parking brake 2 applies braking force to the front wheels FL and FR separately from the braking force by the service brake 1 by driving the EPB motor 10 as an electric actuator provided in the caliper 13 based on the control of the EPB-ECU 9. Provides braking force. Therefore, in an embodiment in which the EPB motor 10 is provided in the rear wheels RL and RR, as shown in FIG. Parking braking force and both can be provided.

FIG. 2 is an exemplary and schematic cross-sectional view showing the configuration of a brake device provided on the rear wheels RL and RR of the vehicle according to the embodiment. FIG. 2 shows a specific example of the structure inside the caliper 13 of the rear wheels RL and RR.

The mechanism by which the service braking force of the service brake 1 increases or decreases is as follows.

As shown in FIG. 2, in the embodiment, the body 14 of the wheel cylinder 6 is provided with a hole 14b for introducing brake fluid into the hollow part 14a inside the body 14. A piston 19 that can reciprocate along the inner peripheral surface of the body 14 is provided in the hollow portion 14a. The piston 19 has a cylindrical shape with a bottom, and a brake pad 11 facing the brake disc 12 is provided at the bottom of the piston 19 .

Here, a seal member 22 is provided inside the body 14 of the wheel cylinder 6 to prevent brake fluid from leaking outside between the outer peripheral surface of the piston 19 and the inner peripheral surface of the body 14. . Thereby, the hydraulic pressure generated in the hollow portion 14a is applied to the end surface of the piston 19 on the opposite side from the brake pad 11.

With the structure described above, when the brake pedal 3 is depressed to operate the service brake 1, hydraulic pressure from the brake fluid is generated in the hollow portion 14a, and the brake pad 11 is pressed in the direction (in the paper of FIG. 2). The piston 19 moves in the left direction). When the piston 19 moves in the direction of pressing the brake pad 11, the brake pad 11 contacts and is pressed against the brake disc 12, and a regular braking force due to frictional force is applied to the wheel corresponding to the brake disc 12. .

Conversely, when the operation of the service brake 1 is to release the brake pedal 3, the hydraulic pressure in the hollow portion 14a decreases, and the pressure on the brake pad 11 is released (toward the right in the paper of FIG. 2). ) the piston 19 moves. Then, when the piston 19 moves in the direction of releasing the pressure on the brake pad 11, the pressing force of the brake pad 11 against the brake disc 12 is weakened, and the braking force applied to the wheel corresponding to the brake disc 12 is reduced. . Note that when the brake pad 11 is completely separated from the brake disc 12, the regular braking force applied to the brake disc 12 becomes zero.

On the other hand, the mechanism by which the parking braking force by the electric parking brake 2 increases or decreases is as follows.

As shown in FIG. 2, in the embodiment, the EPB motor 10 is fixed to the body 14 of the wheel cylinder 6. A spur gear 15 is connected to the drive shaft 10a of the EPB motor 10. As a result, when the EPB motor 10 is driven and the drive shaft 10a rotates, the spur gear 15 also rotates around the drive shaft 10a.

Further, a spur gear 16 having a rotating shaft 17 is meshed with the spur gear 15 . The rotating shaft 17 is located at the rotation center of the spur gear 16, and is supported by an O-ring 20 and a bearing 21 provided in the insertion hole 14c when inserted into the insertion hole 14c of the body 14 of the wheel cylinder 6. has been done.

Here, a male thread groove 17a is formed on the outer circumferential surface of the end of the rotating shaft 17 on the side opposite to the spur gear 16. This male thread groove 17a is screwed into a female thread groove 18a provided on the inner circumferential surface of a bottomed cylindrical linear motion member 18 that reciprocates inside the piston 19. As a result, when the spur gear 15 rotates due to the drive of the EPB motor 10, the rotating shaft 17 rotates together with the spur gear 16, and the linear motion member 18 rotates on the rotating shaft 17 due to the engagement between the male thread groove 17a and the female thread groove 18a. reciprocating in the axial direction.

Note that the linear motion member 18 has a rotation prevention structure in relation to the rotating shaft 17, so that it does not rotate together with the rotating shaft 17 even if the rotating shaft 17 rotates. Similarly, the piston 19 also has a rotation prevention structure in relation to the linearly moving member 18, so that even if the linearly moving member 18 rotates around the rotating shaft 17, it will not rotate together with the linearly moving member 18. It has a structure.

In this way, the embodiment is provided with a motion conversion mechanism that converts the rotation of the EPB motor 10 into reciprocating movement of the linear motion member 18 inside the piston 19. Note that when the drive of the EPB motor 10 is stopped, the direct-acting member 18 is configured to stop at the same position due to the frictional force caused by the engagement between the male thread groove 17a and the female thread groove 18a.

With the above structure, when the EPB motor 10 rotates in the forward direction during operation of the electric parking brake 2, the linear motion member 18 moves in a direction that abuts against the piston 19 (to the left in the plane of the paper in FIG. 2). Then, when the linear motion member 18 and the piston 19 abut with the brake pad 11 pressed against the brake disc 12, the piston 19 is supported by the linear motion member 18. Therefore, even if the brake pedal 3 (see FIG. 1) is released and the hydraulic pressure in the hollow portion 14a decreases, the parking braking force applied to the wheels is maintained (locked).

Conversely, when the EPB motor 10 rotates in the opposite direction, the direct-acting member 18 moves in a direction away from the piston 19 (to the right in the paper of FIG. 2). When the direct-acting member 18 separates from the piston 19, the piston 19 presses the brake pad 11 against the brake disc 12, and the parking braking force applied to the wheels is gradually released. I'm going to go.

In this way, in the embodiment, the service brake 1 and the electric parking brake 2 share a part of the mechanism for applying braking force to the rear wheels RL and RR.

Returning to FIG. 1, the ESC-ECU 8 is configured as a microcomputer equipped with, for example, a processor and a memory, and controls the hydraulic pressure control circuit 7 by having the processor execute a program stored in the memory or the like. realize various functions. The ESC-ECU 8 is communicably connected to the EPB-ECU 9 via an in-vehicle network such as a CAN (Controller Area Network).

Further, like the ESC-ECU 8, the EPB-ECU 9 is also configured as a microcomputer equipped with a processor, memory, etc., and controls the EPB motor 10 by executing a program stored in the memory etc. Achieve various functions to

Here, in the embodiment, the EPB-ECU 9 can use various information to control the EPB motor 10. For example, the EPB-ECU 9 receives the output of the load sensor 23 that detects the load applied to the wheels (particularly the drive wheels), the output of the wheel speed sensor 24 that detects the rotational speed of each wheel of the vehicle, and the The output of the longitudinal acceleration sensor 25 that detects the acceleration of the EPB motor 10 can be used to control the EPB motor 10.

In the embodiment, the wheel speed sensors 24 include a wheel speed sensor 24FL that detects the rotational speed of the front wheel FL, a wheel speed sensor 24FR that detects the rotational speed of the front wheel FR, and a wheel that detects the rotational speed of the rear wheel RL. Four speed sensors 24RL and a wheel speed sensor 24RR that detects the rotational speed of the rear wheels RR are provided.

Further, in the embodiment, the EPB-ECU 9 can also use information acquired from a drive system ECU 30 that controls a drive source 31 such as an engine provided in the vehicle to control the EPB motor 10. The information acquired from the drive system ECU 30 is, for example, information regarding the driving force generated by the drive source 31 under the control of the drive system ECU 30. Like the ESC-ECU 8 described above, the drive system ECU 30 is also communicably connected to the EPB-ECU 9 via an in-vehicle network or the like.

By the way, conventionally, when a vehicle is stopped due to the parking braking force generated by the electric parking brake 2, the parking braking force is released in response to an acceleration operation to accelerate the vehicle, such as DAR (Drive Away Release). A technique called In such conventional technology, on the premise that all drive wheels of the vehicle are in contact with the ground, the driving force generated by the drive source 31 in response to an acceleration operation exceeds a predetermined threshold value depending on the gradient of the road surface. This is generally used as a trigger to start releasing the parking braking force.

However, on a predetermined road surface such as an uphill road with many bumps, it is also assumed that the vehicle is stopped by the parking braking force with at least one wheel not in contact with the ground. If a floating wheel that is not in contact with the ground is the driving wheel, and the parking braking force is released using the general DAR as described above, the actual driving force that is sufficient to compensate for the decrease in parking braking force will not be transmitted to the road surface. , for example, there is a risk that unintended vehicle behavior may occur, such as sliding downhill on an uphill road.

Therefore, the EPB-ECU 9 according to the embodiment executes a predetermined control program stored in a memory or the like by a processor, and realizes a brake control device 300 having functions as shown in FIG. To suppress unintended vehicle behavior that may occur when parking braking force is released in response to an acceleration operation.

Figure 3 is an exemplary block diagram showing the functions of the brake control device 300 according to an embodiment. In an embodiment, some or all of the functions shown in Figure 3 may be realized by dedicated hardware (circuitry).

As shown in FIG. 3, the brake control device 300 according to the embodiment includes a control data acquisition section 301 and an actuator control section 302.

The control data acquisition unit 301 acquires the output of the load sensor 23 or the wheel speed sensor 24. The output of the load sensor 23 or the wheel speed sensor 24 can be used to identify the grounding state indicating whether or not the driving wheels of the vehicle are in contact with the ground. Further, the control data acquisition unit 301 acquires the output of the longitudinal acceleration sensor 25, and also acquires data indicating the driving force generated by the drive source 31 from the drive system ECU 30.

The actuator control unit 302 controls the electric parking brake 2 by controlling the EPB motor 10. For example, in order to control the parking braking force generated by the electric parking brake 2, the actuator control unit 302 can rotate the EPB motor 10 in the forward direction, rotate it in the reverse direction, or stop it.

Here, in the embodiment, the actuator control unit 302 is configured to obtain data acquired by the control data acquisition unit 301 when an acceleration operation is performed on a stopped vehicle due to parking braking force to accelerate the vehicle. The ground contact state of the driving wheels is determined based on the output of the load sensor 23 or the wheel speed sensor 24.

For example, if it is determined based on the output of the load sensor 23 that there is a drive wheel on which a load less than a threshold value is applied, or based on the output of the wheel speed sensor 24, the actuator control unit 302 determines that the drive wheel is spinning. If it is determined that this has occurred, the drive wheel is configured to identify that it corresponds to a floating wheel that is not in contact with the ground.

The actuator control unit 302 is configured to control the electric parking brake 2 to release the parking braking force using different control methods depending on the ground contact state identified by the above method.

More specifically, when it is determined that all the drive wheels are in contact with the ground, the actuator control unit 302 determines that the driving force acquired by the control data acquisition unit 301 is similar to the general DAR as described above. The system is configured to start releasing the parking braking force when a threshold value corresponding to the slope of the road surface, which is set on the premise that all drive wheels are in contact with the ground, is exceeded as a trigger. Note that the slope of the road surface can be estimated based on the output of the longitudinal acceleration sensor 25 acquired by the control data acquisition unit 301.

On the other hand, as mentioned above, if at least one drive wheel corresponds to a floating wheel that is not in contact with the ground, the parking braking force is released using the above threshold set on the assumption that all drive wheels are in contact with the ground. Determining the timing to start may cause unintended vehicle behavior.

Therefore, when at least one drive wheel is identified as a floating wheel, the actuator control unit 302 sets a threshold value for determining the timing to start releasing the parking braking force when all drive wheels are in contact with the ground. The configuration is such that the correction is made larger than the threshold value set on the premise that this is the case.

For example, the actuator control unit 302 corrects the threshold value based on the following equation.

Threshold value = Base × Total driving force / (Total driving force - Driving force loss)

In the above equation, the base is a threshold value corresponding to the slope of the road surface, which is set on the assumption that all drive wheels are in contact with the ground, similar to the general DAR described above.

In the above equation, the total driving force is a value indicating the driving force generated by the drive source 31, and the driving force loss is the actual driving force transmitted to the road surface due to the presence of floating wheels. This value indicates force loss.

For example, assume a situation where the drive source is generating 20 driving forces, and the driving forces are equally distributed to the left and right wheels. In this situation, if one wheel of a four-wheel drive vehicle (i.e. 5 driving forces per wheel) is a floating wheel, the threshold is: Base x 20/(20-5) = Base x 4/3. Calculated using the formula. Also, if one wheel (drive wheel) of a two-wheel drive (that is, the driving force per wheel is 10) is a floating wheel, the threshold value is base x 20/(20-10) = base x 2. Calculated using the formula.

In this manner, in the embodiment, the actuator control unit 302 corrects the threshold value according to the installation state of the drive wheels. Then, the actuator control unit 302 controls the electric parking brake 2 so that release of the parking braking force begins at the timing when the driving force generated by the drive source 31 in response to the acceleration operation exceeds the corrected threshold value. As a result, even in a situation where at least one drive wheel is not in contact with the ground, release of the parking braking force can begin once sufficient actual driving force is secured to avoid unintended vehicle behavior.

However, for example, in a vehicle with an LSD (Limited Split Differential) function, if one of the left and right drive wheels corresponds to a floating wheel that is not in contact with the ground, the parking braking force generated on the floating wheel is accelerated. If it is released in response to this, the driving force will be intensively transmitted only to the floating wheels, and there is a risk that the driving force transmitted to the driving wheels that are in contact with the ground will be reduced.

Therefore, in the embodiment, when the driving wheels include a floating wheel that is not in contact with the ground, the actuator control unit 302 controls the electric parking brake so as to release only the parking braking force generated on the driving wheels other than the floating wheel. 2 can be controlled.

Furthermore, in the embodiment, even if the vehicle starts by releasing the parking braking force (on the drive wheels other than the floating wheels), the actuator control unit 302 continues to operate the floating wheels until the floating wheels touch the ground. The electric parking brake 2 is configured to be controllable so as to generate a parking braking force.

Note that, as described above, in the embodiment, the installation state of the driving wheels is specified based on the output of the load sensor 23 or the wheel speed sensor 24 acquired by the control data acquisition unit 301. Therefore, if an abnormality occurs in only one of the load sensor 23 and wheel speed sensor 24, it is possible to identify the current installation state of the drive wheels based on the output of the other sensor. If an abnormality occurs in both the sensor 23 and the wheel speed sensor 24, it becomes difficult to identify the current installation state of the drive wheels.

Therefore, in the embodiment, when an abnormality occurs in the load sensor 23 and the wheel speed sensor 24, the actuator control unit 302 performs a control operation at a past (recent) timing that satisfies the condition that the vehicle has not started until now. Based on the output of the load sensor 23 or the wheel speed sensor 24 acquired by the data acquisition unit 301, the current ground contact state of the driving wheels can be identified.

Based on the above configuration, in the embodiment, as an example, the parking braking force is released in accordance with the acceleration operation in accordance with a timing chart as shown in FIG. 4 below.

FIG. 4 is an exemplary timing chart for explaining an example of releasing the parking braking force in response to an acceleration operation performed in the embodiment. The example shown in FIG. 4 assumes a situation where the vehicle is stopped by the parking braking force on a predetermined road surface, such as an uphill road with many bumps, in a state where at least one drive wheel is not in contact with the ground. .

In the example shown in FIG. 4, a solid line L411 indicates a temporal change in the parking braking force in the embodiment, and a two-dot chain line L411a indicates a temporal change in the parking braking force in the comparative example. Note that the comparative example corresponds to an example in which general DAR is executed without considering the ground contact state of the drive wheels at all.

Further, in the example shown in FIG. 4, a solid line L412 indicates a temporal change in the actual driving force in the embodiment, and a dashed-dotted line L412a indicates a temporal change in the actual driving force in the comparative example. The actual driving force is the driving force that is actually transmitted from the wheels to the road surface in accordance with the driving force generated by the drive source 31.

Note that in the example shown in FIG. 4, a solid line L420 indicates a temporal change in the driving force generated by the driving source 31. The time change indicated by the solid line L420 is common to both the embodiment and the comparative example.

In the example shown in FIG. 4, the driving force generated by the driving source 31 starts to increase at timing t401 in response to an acceleration operation for a vehicle stopped by the parking braking force (see solid line L420). Then, the driving force generated by the driving source 31 reaches a predetermined threshold Th401 at timing t402 (see solid line L420).

Here, the threshold Th401 is a threshold corresponding to the above-mentioned base, which is used as a trigger to start releasing the parking braking force in the comparative example. Therefore, in the comparative example, at timing t402 when the driving force generated by the driving source 31 reaches the threshold value Th401, all the driving wheels are in contact with the ground, so that the driving force is sufficient to avoid unintended vehicle behavior. The release of the parking braking force starts (see the two-dot chain line L411a) on the premise that the parking braking force is secured (see the one-dot chain line L412a).

However, if at least one driving wheel is not in contact with the ground, sufficient actual driving force to avoid unintended vehicle behavior is not generated at timing t402 (see solid line L412). Therefore, in the embodiment, the threshold value used as a trigger to start releasing the parking braking force is corrected to a threshold value Th402 larger than the threshold value Th401 using the method described above.

According to the above correction, at timing t403 when the driving force generated by the drive source 31 reaches the threshold Th402, sufficient driving force is ensured to avoid unintended vehicle behavior ( (See solid line L412). Therefore, in the embodiment, even if the release of the parking braking force is started at timing t403 (see solid line L411), unintended vehicle behavior such as sliding downhill does not occur. Then, when timing t403 is exceeded, the vehicle starts moving. Note that the release of the parking braking force is completed at timing t404 (see solid line L411).

A series of processes executed by the brake control device 300 in order to release the parking braking force in response to an acceleration operation in the manner described above will be described in more detail below.

FIG. 5 is an exemplary flowchart showing a series of processes that the brake control device 300 according to the embodiment executes when releasing the parking braking force in response to an acceleration operation. The series of processes shown in FIG. 5 starts when an acceleration operation is performed on a stopped vehicle due to parking braking force.

As shown in FIG. 5, in the embodiment, first, in step S501, the actuator control unit 302 of the brake control device 300 estimates the slope of the road surface on which the vehicle is currently stopped. The slope of the road surface can be estimated based on the output of the longitudinal acceleration sensor 25 acquired by the control data acquisition unit 301.

Then, in step S502, the actuator control unit 302 of the brake control device 300 determines a threshold value to be compared with the driving force generated by the driving source 31 in order to determine the start of releasing the parking braking force. This threshold value corresponds to the above-mentioned base and is determined according to the slope of the road surface on the premise that all drive wheels are in contact with the ground.

Then, in step S503, the actuator control unit 302 of the brake control device 300 identifies the ground contact state of the drive wheels. The ground contact state can be specified based on the output of the load sensor 23 or the wheel speed sensor 24 acquired by the control data acquisition unit 301.

Then, in step S504, the actuator control unit 302 of the brake control device 300 determines whether at least one drive wheel corresponds to a floating wheel that is not in contact with the ground, based on the ground contact state identified in step S503 above. Determine.

If it is determined in step S504 that at least one drive wheel corresponds to a floating wheel, the process proceeds to step S505.

Then, in step S505, the actuator control unit 302 of the brake control device 300 calculates the loss of the actual driving force transmitted from the drive wheels to the road surface. Note that the actual driving force loss corresponds to the driving force loss described above.

Then, in step S506, the actuator control unit 302 of the brake control device 300 corrects the threshold determined in step S502 above based on the actual driving force loss calculated in step S505 above. The specific method of correction has already been explained using equations, so the explanation will be omitted here.

When the process of step S506 is completed, the process advances to step S507. Note that even if it is determined in step S504 that all the drive wheels are in contact with the ground, the process proceeds to step S507 (in this case, the processes in steps S505 and S506 described above are skipped).

In step S507, the actuator control unit 302 of the brake control device 300 determines whether the driving force generated by the drive source 31 exceeds the threshold determined in step S502 described above or the threshold after correction in step S506 described above. Determine whether The driving force generated by the drive source 31 can be acquired from the drive system ECU 30 via the control data acquisition unit 301.

The determination process in step S507 is repeatedly executed until it is determined that the driving force exceeds the threshold value. If it is determined in step S507 that the driving force exceeds the threshold value, the process proceeds to step S508.

In step S508, the actuator control unit 302 of the brake control device 300 starts releasing the parking braking force. Thereby, it is possible to start releasing the parking braking force in response to securing sufficient driving force to avoid unintended vehicle behavior. Then, the process ends.

As described above, the brake control device 300 according to the embodiment includes a control data acquisition section 301 and an actuator control section 302. The control data acquisition unit 301 acquires the output of the load sensor 23 or the wheel speed sensor 24, which is a sensor that detects information indicating the ground contact state of the driving wheels of the vehicle. The actuator control unit 302 is configured to obtain data acquired by the control data acquisition unit 301 when an acceleration operation is performed on a stopped vehicle to accelerate the vehicle due to the parking braking force generated by the electric parking brake 2. The electric parking brake 2 is controlled to specify the ground contact state of the drive wheels based on the output of the ground load sensor 23 or the wheel speed sensor 24, and to release the parking braking force using different control methods depending on the specified ground contact state. do.

According to the above configuration, when releasing the parking braking force in response to an acceleration operation, the ground contact state of the driving wheels is taken into consideration. Therefore, it is possible to suppress unintended vehicle behavior that may occur when the parking braking force is released in response to an acceleration operation.

Further, in the embodiment, the above control is realized by the electric parking brake 2 instead of the service brake 1. In order to achieve control similar to the above control using the service brake 1, the pump of the service brake 1 must be operated at all times, which is inconvenient in terms of fuel efficiency and the lifespan of the motor that drives the pump. There is. On the other hand, in the embodiment, the above control can be achieved without any inconvenience by simply controlling the EPB motor 10 of the electric parking brake 2 by rotating it in the opposite direction.

Here, in the embodiment, the actuator control unit 302 controls the parking braking force when the driving force generated by the drive source of the vehicle in response to the acceleration operation reaches a threshold value determined according to the ground contact state of the driving wheels. The electric parking brake 2 is controlled to start releasing the brake. According to such a configuration, the timing to start releasing the parking braking force can be appropriately adjusted using the threshold value determined according to the ground contact state of the drive wheels so as to suppress unintended vehicle behavior. I can do it.

Furthermore, in the embodiment, when the drive wheels include a floating wheel that is not in contact with the ground, the actuator control unit 302 continuously generates parking braking force on the floating wheel while generating parking braking force on the drive wheels other than the floating wheel. The electric parking brake 2 can be controlled to release the parking braking force applied. According to such a configuration, for example, in a vehicle having an LSD function, driving force is prevented from being intensively transmitted only to the floating wheels, and driving force is reliably transmitted to the driving wheels that are in contact with the ground. can be transmitted.

Further, in the embodiment, the actuator control unit 302 operates the electric parking brake 2 so that even if the vehicle starts, the floating wheel continues to generate parking braking force until the floating wheel touches the ground. Can be controlled. According to such a configuration, even when the vehicle starts, driving force can be reliably transmitted to the drive wheels that are in contact with the ground.

Note that in the embodiment, when an abnormality occurs in both the load sensor 23 and the wheel speed sensor 24, the actuator control unit 302 uses the acquisition unit to acquire the data at a timing in the past that satisfies the condition that the vehicle has not started until now. Based on the acquired output of the load sensor 23 or wheel speed sensor 24, the current ground contact state of the driving wheels is identified. According to such a configuration, even if an abnormality occurs in both the load sensor 23 and the wheel speed sensor 24, past data can be used to release the parking braking force in response to an acceleration operation. Unintended vehicle behavior that may occur can be suppressed.

<Modified example>
Note that the electric parking brake 2 according to the embodiment described above is an electric parking brake compatible with a disc brake, but this is just an example. The technology of the present disclosure can also be applied to an electric parking brake that is compatible with other brakes than disc brakes, such as drum brakes.

Further, in the embodiment described above, a configuration is exemplified in which a desired effect is obtained by correcting the threshold value with which the driving force generated by the driving source 31 is compared according to the installation state of the driving wheels. However, as a modification, a configuration can be considered in which the desired effect is obtained by changing the slope of the release of the parking braking force according to the ground contact state of the drive wheels, as shown in FIG. 6 below. In addition, below, the description is abbreviate|omitted by attaching|subjecting the same code|symbol about the same component as the embodiment mentioned above.

FIG. 6 is an exemplary timing chart for explaining the release of parking braking force in response to an acceleration operation that may be performed in a modification of the embodiment. Similarly to the example shown in FIG. 4 described above, the example shown in FIG. 6 is also similar to the example shown in FIG. This assumes a situation where the vehicle is stopped.

In the example shown in FIG. 6, a solid line L611 indicates a temporal change in the parking braking force in the modified example, and a two-dot chain line L611a indicates a temporal change in the parking braking force in the comparative example. Note that the comparative example corresponds to an example in which general DAR is executed without considering the grounding state of the driving wheels at all, similar to the comparative example illustrated for explanation of the embodiment described above.

Further, in the example shown in FIG. 6, a solid line L612 indicates a time change in the actual driving force in the embodiment, and a dashed-dotted line L612a indicates a time change in the actual driving force in the comparative example. The actual driving force is the driving force that is actually transmitted from the wheels to the road surface in accordance with the driving force generated by the drive source 31.

Note that in the example shown in FIG. 6, a solid line L620 indicates a temporal change in the driving force generated by the driving source 31. In the example shown in FIG. The time change indicated by the solid line L620 is common to both the embodiment and the comparative example.

In the example shown in FIG. 6, the driving force generated by the driving source 31 starts to increase at timing t601 in response to an acceleration operation for a vehicle stopped by the parking braking force (see solid line L620). Then, the driving force generated by the driving source 31 reaches a predetermined threshold Th601 at timing t602 (see solid line L620).

Here, the threshold Th601 is a threshold corresponding to the above-mentioned base, which is used as a trigger to start releasing the parking braking force in the comparative example. Therefore, in the comparative example, at timing t602 when the driving force generated by the driving source 31 reaches the threshold value Th601, all the driving wheels are in contact with the ground, which is sufficient to avoid unintended vehicle behavior. On the premise that the parking braking force is secured (see one-dot chain line L612a), the parking braking force starts to be released (see two-dot chain line L611a). In the comparative example, the release of the parking braking force is completed at timing t603 (see the two-dot chain line L611a).

Here, the modified example makes the slope of the parking braking force release gentler than the comparative example without changing the threshold itself used as a trigger to start releasing the parking braking force, thereby preventing unintended vehicle damage. Achieve behavior control. That is, in the modified example, the release of the parking braking force is started at timing t602, as in the comparative example, but in the comparative example, the parking braking force is released at timing t604, which is later than the timing t603 when the release of the parking braking force is completed. The slope of the release of the parking braking force is adjusted so that the release of the parking braking force is completed (see solid line L611).

According to the above adjustment, the state in which the parking braking force remains remains for a longer period of time than in the comparative example, so that unintended vehicle behavior can be suppressed.

In this manner, in the modified example shown in FIG. 6, the gradient of release of the parking braking force is adjusted depending on the ground contact state of the driving wheels. According to such a configuration, unintended vehicle behavior can be suppressed by, for example, releasing the parking braking force more gently when at least one drive wheel is not in contact with the ground than when all drive wheels are in contact with the ground. In this way, the parking braking force can be released at a gradient that corresponds to the ground contact state of the driving wheels.

Note that the technology of the present disclosure also includes a technology that obtains a desired effect by performing both the threshold correction according to the embodiment described above and the gradient adjustment according to the modification described above.

Although the embodiments and modifications of the present disclosure have been described above, the embodiments and modifications described above are merely examples, and are not intended to limit the scope of the invention. The novel embodiments and modified examples described above can be implemented in various forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. Furthermore, the above-described embodiments and modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.

2 Electric parking brake 23 Load sensor 24, 24FL, 24FR, 24RL, 24RR Wheel speed sensor 31 Drive source 300 Brake control device 301 Control data acquisition unit (acquisition unit)
302 Actuator control section (control section)

Claims (5)

an acquisition unit that acquires the output of a sensor that detects information indicating the ground contact state of the driving wheels of the vehicle;
When an acceleration operation is performed for accelerating the vehicle that is stopped due to the parking braking force generated by the electric parking brake, the above-mentioned method is performed based on the output of the sensor acquired by the acquisition unit. a control unit that controls the electric parking brake to specify the ground contact state of the driving wheels and release the parking braking force using different control methods depending on the specified ground contact state;
Equipped with
The control unit is a brake control device that adjusts a gradient of release of the parking braking force according to the grounding state of the drive wheels . The control unit is configured to release the parking braking force when the driving force generated by the drive source of the vehicle in response to the acceleration operation reaches a threshold determined according to the ground contact state of the driving wheels. controlling the electric parking brake to initiate;
The brake control device according to claim 1. When the driving wheels include floating wheels that are not in contact with the ground, the control unit may control the parking brake force generated on the driving wheels other than the floating wheels while continuously generating the parking braking force on the floating wheels. controlling the electric parking brake to release the braking force;
The brake control device according to claim 1 or claim 2 . The control unit controls the electric parking brake so that the floating wheel continues to generate the parking braking force until the floating wheel touches the ground even when the vehicle starts moving.
The brake control device according to claim 3 . When an abnormality occurs in the sensor, the control unit controls the drive based on the output of the sensor acquired by the acquisition unit at a past timing that satisfies a condition that the vehicle has not started until now. Determine the current ground contact status of the wheels,
The brake control device according to any one of claims 1 to 4 .

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